Techniques are under development in which while changing the temperature of a sample, the weight change and the quantity of generated and absorbed heat are quantified thereby analyzing a thermal decomposition reaction of the sample and the like. Of those, thermogravimetry (hereinafter referred to as “TG”) is a technique that is generally used for evaluating the heat resistance property of a sample and analyzing a heat decomposition reaction thereof, in which while the temperature of the sample is changed, the change in the weight of the sample is measured. This measurement can be performed using a thermogravimeter. Further, differential scanning calorimetry (hereinafter referred to as “DSC”) is a technique for capturing the change in the temperature and the enthalpy caused by melting and phase transition of a sample (heat of fusion, heat of transition) and the like, thereby quantifying the temperature of reactions such as glass transition and hardening reaction; the heat of reaction; and the like. The DSC can be performed using a differential scanning calorimeter.
Similar techniques to the DSC includes differential thermal analysis (hereinafter referred to as “DTA”) in which while the temperature of a sample is changed, the relative temperature change of a sample caused by phase transition, reactions, and the like with respect to a reference material is measured. In DSC, a heat sink is provided in terms of the device structure, and the generated and absorbed heat can be quantified by measuring the amount of heat moving between the sample and the heat sink. To the contrary, in DTA, although the transition temperature and the like of the sample can be measured, it is assumed to be difficult in terms of the structure, to measure generated and absorbed heat such as heat of transition.
Here, the principle of DSC will be described with reference to FIG. 11. FIG. 11 is a diagram showing the structure of a typical differential scanning calorimeter. A sample container loaded with a sample and a sample container loaded with a reference material are fixed to a heat sink through coupling members having a predetermined thermal resistance. The sample and the reference material are placed inside a furnace provided with a heat coil, and the temperature inside the furnace is controlled using a control unit not shown. A differential thermocouple is provided to measure the temperature difference ΔT between the temperature TS of the sample and the temperature TR of the reference material; the ΔT is calculated by dividing the voltage VSR at both ends of the differential thermocouple by the Seebeck coefficient inherent to the material of the thermocouple.
Provided that the temperature of the heat sink is TH, the heat flow dqs/dt, that is, the quantity of heat flowing from the heat sink to the sample per unit time is expressed by Equation (1).
                              [                      Equation            ⁢                                                  ⁢            1                    ]                ⁢                                                                                                                          d              ⁢                                                          ⁢                              q                S                                                    d              ⁢                                                          ⁢              t                                =                                    1              R                        ⁢                          (                                                T                  H                                -                                  T                  S                                            )                                      ,                                      (          1          )                ,            
where R is a thermal resistance between the sample and the heat sink.
Similarly, the heat flow dqR/dt from the heat sink to the reference material is expressed by Equation (2).
                              [                      Equation            ⁢                                                  ⁢            2                    ]                ⁢                                                                                                                          d              ⁢                                                          ⁢                              q                S                                                    d              ⁢                                                          ⁢              t                                =                                    1              R                        ⁢                          (                                                T                  H                                -                                  T                  S                                            )                                      ,                            (        2        )            
Accordingly, the relationship between ΔT and the difference dΔq/dt between the heat flow from the heat sink to the reference material and the heat flow from the heat sink to the sample can be expressed by Equation (3), in which Equation (2) is subtracted from Equation (1).
                              [                      Equation            ⁢                                                  ⁢            3                    ]                ⁢                                                                                                            d            ⁢                                                  ⁢            Δ            ⁢                                                  ⁢            q                                d            ⁢                                                  ⁢            t                          =                                                            d                ⁢                                                                  ⁢                                  q                  S                                                            d                ⁢                                                                  ⁢                t                                      -                                          d                ⁢                                                                  ⁢                                  q                  R                                                            d                ⁢                                                                  ⁢                t                                              =                                                    1                R                            ⁢                              (                                                      T                    R                                    -                                      T                    S                                                  )                                      =                                          -                                  1                  R                                            ⁢              Δ              ⁢                                                          ⁢              T                                                          (        3        )            
FIGS. 12(A) and 12(B) show the result of DSC during an endothermic reaction of the sample. The rise of the sample temperature Ts is retarded during a period between the times t1 and t2 as shown in FIG. 12(A). As shown in FIG. 12(B), a peak of the difference ΔTP between the temperatures of the sample and the reference material is observed in the same period. Note that the peak ΔTP here is the difference between the temperature difference prior to the start of the endothermic reaction and the temperature at a time when the absorbed heat flow is maximized. Both sides of Equation (3) are integrated with respect to the period between the times t1 and t2 to obtain the following Equation (4).
                              [                      Equation            ⁢                                                  ⁢            4                    ]                ⁢                                                                                                            ∫                          t              1                                      t              2                                ⁢                                                                      d                  ⁢                                                                          ⁢                  Δ                  ⁢                                                                          ⁢                  q                                                  d                  ⁢                                                                          ⁢                  t                                            ·                                                          ⁢              d                        ⁢                                                  ⁢            t                          =                              -                          1              R                                ⁢                                    ∫                              t                1                                            t                2                                      ⁢                          Δ              ⁢                                                          ⁢                              T                ·                                                                  ⁢                d                            ⁢                                                          ⁢              t                                                          (        4        )            
The left side of Equation (4) is the amount of heat Q absorbed by the sample during the period between times t1 and t2, whereas
      ∫          t      1              t      2        ⁢      Δ    ⁢                  ⁢          T      ·                          ⁢      d        ⁢                  ⁢    t  in the right side is the area corresponding to the peak portion hatched in FIG. 12(B). Accordingly, the area of the peak portion is in proportion to the amount of heat Q absorbed by the sample.
Note that the coefficient R in Equation (3) that is used for determining the heat flow dΔq/dt absorbed by the sample from the temperature difference ΔT can be calculated for example from the relationship between the area of the peak portion of the temperature difference ΔT obtained by performing a DSC measurement on a material which absorbs a known amount Q by melting and the amount of absorbed heat Q.
On the other hand, DTA does not involve a structure corresponding to the heat sink in DSC. Accordingly, although the transition temperature can be found from the peak of the absorbed heat, the temperature difference ΔT cannot be converted into the amount of absorbed heat Q.
In recent years, devices for simultaneously performing measurements using TG and DSC or DTA that have been described above. For example, such an analysis, in which while weight change resulted from solvent evaporation from a sample or thermal decomposition is captured by TG, the resultant endothermic/exothermic phenomenon is captured by DSC or DTA at the same time has become possible. These analyses and relevant devices are referred to as TG-DSC or TG-DTA. Such an analysis is also referred to as simultaneous thermal analysis (STA).
A typical structure of a TG-DSC is disclosed, for example, in EP 0405153 B (PTL 1). A device for thermal analysis disclosed in PTL 1 has sample holders capable of carrying a sample and a reference material, which holders are provided on the tip of one supporting rod extending upward from a balance mechanism. The sample holders include a sample container for carrying a sample and a sample container for carrying a reference material on a heat sink. Accordingly, a structure of DSC is employed in which the difference between the heat flow from a heat sink to a sample and the heat flow from the heat sink to a reference material is detected.
On the other hand, a typical structure of TG-DTA is disclosed, for example, in JP 3127043 B (PTL 2) and JP 3241427 B (PTL 3). PTL 2 discloses a thermogravity detector (TG-DTA) capable of measuring the weight difference and the temperature difference between a sample and a reference material on pans placed on vertical supporting rods of an upright (vertical) differential balance. DTA can be performed by measuring the temperature difference between the sample and the reference material; however, a heat sink for measuring the difference between the heat flow from the heat sink to the sample and the heat flow from the heat sink to the reference material is not provided. Thus, the TG-DTA does not have a structure of DSC.
PTL 3 discloses a device for thermal analysis, capable of measuring the weight difference and the temperature difference between a sample and a reference material placed on respective holders provided on the tip of two horizontally extending beams in a horizontal differential balance (TG-DTA). DTA can be performed by measuring the temperature difference between the sample and the reference material; however, a heat sink for measuring the difference between the heat flow from the heat sink to the sample and the heat flow from the heat sink to the reference material is not provided. Thus, the TG-DTA does not have a structure of DSC as with PTL 2.